The U.S. Pat. No. 4,635,890, issued Jan. 13, 1989 to Matsuda, et al., discloses a lock mechanism for an adjustable seat wherein the seat is mounted on right and left slide rails slidable on right and left guide rails so that the position of the seat is adjustable back and forth. Right and left lock mechanisms are mounted on the right and left slide rails, respectively, for locking relative movement between a right or left pair of the slide and guide rails.